This proposal may be regarded as part of a general effort to develop a comprehensive data base and an understanding of the phenomenon known as tinnitus (in patients with sensorineural losses caused by noise trauma or exposure). Since masking noises are utilized to obscure tinnitus (Vernon, 1975), the first series of perceptual studies involve the masking of tinnitus. We plan to explore the temporal course of the masking of tinnitus by broadband and filtered noise, to correlate the annoyance of the tinnitus with the temporal course of masking, to detemine the duty cycle, temporal shape, and bandwidth of the noise required to obscure the tinnitus, to measure "residual inhibition" in terms of the noise required to mask the reportedly "softer" tinnitus that often follows noise exposure, and to determine the subjective variability of tinnitus. In a second series of psychophysical studies, tuning curves and suppression regions will be determined pre- and post-noise exposure. The effect of noise exposure on normal observers and on those with sensorineural hearing loss provides a striking comparison. Exposure to noise can produce tinnitus in normals whereas it can inhibit tinnitus in patients with sensorineural loss. Following noise exposure, the normal observer's tuning curve widens and may thereby cause an imbalance between response and suppression mechanisms, resulting in tinnitus. Since the sensorineural patient's tuning curve may be broad prior to noise exposure, the exposure itself may not affect his tuning curves. The main thrust of this proposal is to develop an understanding of the way in which auditory dysfunction produces tinnitus. However, by-products of the experimental approach include the data needed to begin to evaluate Vernon's tinnitus maskers and to establish an objective test for the existence of tinnitus.